Braking system for a trailer vehicle

ABSTRACT

An electro-pneumatic system including relay valves disposed between a pressure supply inlet and outputs respectively, and having respective control inputs; associated solenoid-operated valves each operable in a first or a second condition respectively to allow or prevent connection of the control input of the relay valves respectively to a pneumatic duct; a solenoid-operated commutation valve having respective first and second conditions in which it connects the pneumatic duct to the control input of the system to receive a braking control pressure or to an inlet/outlet aperture of a second solenoid-operated switching valve; and an electronic control unit (ECU) arranged to control the solenoid valves. The second switching valve has respective first and second conditions in which its inlet/outlet aperture is connected to a discharge passage opening to the outside environment or to the supply inlet.

The present invention relates to a braking system for a trailer vehicle.

More specifically, the invention relates to a braking system for atrailer vehicle which comprises an electro-pneumatic system including apair of relay valves for applying braking pressure to the brakingelements associated with the left and right hand respectively of thetrailer, a plurality of solenoid valves, selectively operable to controlthe relay valves, and an electronic control unit for controlling thesaid solenoid valves in accordance with predetermined modes ofoperation.

One object of the present invention is to provide a braking system ofthe aforesaid type which is very simple and requires fewer solenoidvalves than prior art systems to control the relay valves associatedwith the braking elements or brake actuators.

This and other objects are achieved according to the invention byproviding a braking system the main characteristics of which are claimedin the appended Claim 1.

Further characteristics and advantages of the invention will becomeapparent from the detailed description which follows, provided purely byway of non-limitative example, with reference to the appended drawing,which is an electro-pneumatic circuit diagram for a system according tothe invention.

In FIG. 1, a braking system for a trailer according to the invention isgenerally indicated EBS.

The system EBS comprises an electro-pneumatic braking system, generallyindicated 100 and an associated electronic control unit, indicated ECU.

In the following description of the electro-pneumatic system 100,reference numerals are mostly greater than 100, while certain parts, andin particular certain connectors, have been given reference numbers lessthan 100, corresponding to the numbers conventionally used in the artfor connectors for pneumatic brake systems.

The electro-pneumatic system 100 is provided for installation on atrailer vehicle and has a control input 4 for receiving brake controlpressure from a valve for controlling braking of the trailer vehicle101, installed in the tractor vehicle 102 to which the trailer isattached. The pressure applied in operation to the input 4 of the system100 indicates the desired braking pressure to be applied to thepneumatic braking elements of the trailer.

The system 100 also has a pressure inlet 1-1 for connection to apressure source 103 provided in the trailer, such as a pressure tank.

The system 101 also has first and second outputs 21 and 22 forconnection to the pneumatic braking elements (known per se and not shownin the drawing) associated with the wheels on the left and right siderespectively of the trailer.

The electro-pneumatic braking system 100 includes first and second relayvalves 104 and 105, having respective supply connectors 104 a and 105 aboth connected to the supply inlet 1-1 of the system.

The relay valves 104 and 105 have respective control inputs 104 b and105 b and respective outlets 104 c and 105 c connected to the output 21and the output 22 respectively of the electro-pneumatic system 100.

First and second solenoid-operated on/off valves are indicated 106 and107 respectively in the drawing, and are associated respectively withthe first and second relay valves 104 and 105. These solenoid valves areof a one-way, two-position type and can assume a first condition (shownin FIG. 1) in which they can allow the control inputs 104 b and 105 brespectively of the relay valves 104 and 105 to be connected to a(single) pneumatic duct 108.

The solenoid-operated on/off valves 106 and 107 also have a secondcondition or position, in which they cut off the said control inputs 104b and 105 b of the relay valves 104 and 105 from the duct 108.

The control windings of the solenoid valves 106 and 107 are connected tocorresponding outputs of the electrical control unit ECU.

Two solenoid-operated commutation valves are indicated 109 and 110. Inthe embodiment illustrated, these solenoid valves are of a three-way,two-position type.

The solenoid valve 109 has a first position or condition (shown inFIG. 1) in which it connects the pneumatic duct 108 with the controlinput 4 of the electro-pneumatic braking system 100. It can commute to asecond condition or position in which it connects the pneumatic duct 108with an inlet/outlet aperture 110 a of the solenoid-operated commutationvalve 110. This latter has a first position (illustrated) in which isconnects the said inlet/outlet aperture 110 a to a discharge passage 3opening into the outside environment. In its second position (notshown), the solenoid-operated commutation valve 110 connects the supplyinlet 1-1 with its own inlet/outlet aperture 110 a and thus with thesolenoid valve 109.

The control windings of the solenoid valves 109 and 110 are alsocontrolled by the electronic control unit ECU.

Two electrical pressure transducers, indicated 111 and 112 are providedto emit electrical signals indicating the pressure at the control input4 and at the switching inlet 1-1 of the electro-pneumatic system 100.

Additional pressure transducers 113 and 114 are associated with theoutputs 21 and 22 of this electro-pneumatic system.

Finally, a further pressure transducer 115 is provided to emitelectrical signals indicating the load condition of the trailer. Thistransducer may, for example be associated with the suspension of thetrailer.

The pressure transducers 111-115 are connected to corresponding inputsof the electronic control unit ECU.

In the embodiment illustrated, the electro-pneumatic system 100 has anadditional inlet indicated 1-2. This inlet is provided for connection toan emergency valve for normally receiving pressure from this latter. Theinlet 1-2 is connected to the output 104 c of the relay valve 104 bymeans of a double non-return valve 116 connected to outputs 23 and 24which are intended to be connected to spring operated braking means(known per se and therefore not shown) of the trailer vehicle.

In operation, with the electro-pneumatic system in the condition shownin the drawing, brake-control pressure arriving at the input 4 of thesystem 100 reaches the control inputs 104 b and 105 b of the relayvalves 104 and 105 via the solenoid-operated commutation valve 109 andthe solenoid-operated on/off valves 106 and 107. The relay valves 104and 105 apply a braking pressure to the braking elements connected tothe outputs 21 and 22 of the system 100 which corresponds to the degreeof pressure applied to the control input 4 of the system.

The control unit ECU measures the pressure values signalled by thesensors 111-115.

The unit ECU is set to cause an increase in pressure, when necessary, tothe control input of one or both of the relay valves 104 and 105.

In order to increase pressure at the control input of the relay valve104, for example, the unit ECU controls the solenoid valves 106, 110 toadopt an operating condition in which both solenoid-operated commutationvalves 109 and 110 are in their aforesaid second positions (that is theposition not illustrated in FIG. 1), while the solenoid-operated on/offvalve 106 associated with the relay valve 104 is in the condition shownin the drawing, and the other on/off valve 107 is in the condition inwhich it disconnects the relay valve 105 from the pneumatic duct 108. Inthis condition, the pressure inlet 1-1 is connected to the control input104 b of the relay valve 104, by means of the solenoid valves 109 and110, the pneumatic duct 108 and the solenoid valve 106. This makes itpossible to increase braking pressure to the output 21 of theelectro-pneumatic system 100.

Once the desired pressure is reached at the output 21 (measured by thetransducer 113), the control unit ECU controls the on/off valve 106 tocommute, disconnecting the control input 104 b of the relay valve 104from the pressure supply inlet 1-1.

In order to control a pressure increase to both outputs 21 and 22, theunit ECU controls the solenoid valves 106-110 as described above, exceptthat this time the solenoid valve 107 is also kept in the first,illustrated, position, thereby allowing the control input 105 b of therelay valve 105 also to be connected to the pressure inlet 1-1 of theelectro-pneumatic system. Once the desired braking pressure is reached,both solenoid valves 106 and 107 are commuted.

In a manner similar to that described above, the unit ECU isconveniently arranged to be able, when desirable or necessary, tocontrol a decrease in pressure applied to the control input of one orboth of the relay valves 104 and 105.

Thus, for example, if a decrease in pressure is required at the controlinput 104 b of the relay valve 104, the unit ECU controls the solenoidvalves 106-110 so as to adopt an operating condition in which thesolenoid valve 109 is in the second condition described earlier (that itthe one not shown in the drawing), the solenoid valves 106 and 110 arein the condition shown in the drawing, while the solenoid valve 107 isin the condition which is not shown.

In this condition, the control input 104 b of the relay valve 104 is incommunication with the outside environment via the solenoid valve 106,the pneumatic duct 108, the solenoid valve 109, the inlet/outletaperture 110 a and the exhaust passage 3 of the solenoid valve 110. Oncethe braking pressure 21 has dropped to the desired value, the unit ECUcauses the solenoid valve 106 to commute.

In a similar manner to that described above, the unit ECU can cause acontrolled decrease in pressure to the control inputs of both the relayvalves 104 and 105.

The system described above is not however able to increase pressureapplied to the control input of one relay valve while simultaneouslydecreasing pressure to the control input of the other relay valve.Should such an operation be necessary, the system described above wouldrequire the two operations to be carried out in sequence, with thesecond being carried out after a delay corresponding to the timerequired to complete the first.

This disadvantage is more than compensated for, however, by theremarkable simplicity of construction of the electro-pneumatic system100 described above and, in particular, by the reduced number ofsolenoid valves it requires, as well as by the simplicity with which theunit ECU can control these valves.

Naturally, the principle of the invention remaining unchanged,embodiments and manufacturing details may vary widely from thosedescribed and illustrated purely by way of non-limitative example,without departing thereby from the scope of the invention, as claimed inthe appended Claims.

1. A braking system for a trailer vehicle which comprises: anelectro-pneumatic braking system provided in the trailer vehicle andincluding: a control input for a control pressure the value of which isindicative of a desired braking pressure to be applied to brakingelements of the vehicle; a supply inlet for connection to a pressuresource of the vehicle, first and second outputs respectively forconnection to the braking elements associated with the left and rightside respectively of the vehicle; first and second pneumaticallycontrolled relay valves disposed between said supply inlet and saidfirst and second outputs respectively, and having respective pneumaticcontrol inputs; first and second solenoid-operated on/off valvesconnected between the control input of first and second relay valvesrespectively, and a single, common pneumatic duct, and each operable, ina first and a second condition, respectively, to allow and preventconnection of the control input of the corresponding relay valve to saidcommon pneumatic duct; a first solenoid-operated switching valve havingfirst and second conditions, respectively, in which it couples saidcommon pneumatic duct to the control input and to an inlet/outletaperture of a normally closed second solenoid-operated switching valve,respectively, said second solenoid-operated switching valve having firstand second conditions respectively in which its inlet/outlet aperture iscoupled to a discharge passage opening to the outside environment and tosaid supply inlet, respectively; and an electronic control unit arrangedto control said solenoid valves in accordance with predetermined modesof operation and operable selectively to obtain: an increase in pressureapplied to the control input of at least one relay valve by controllingsaid solenoid valves so as to achieve a first operating condition inwhich both solenoid-operated switching valves are in said secondcondition, while the solenoid-operated on/off valve, associated with therelay valve is in first condition; or a controlled decrease in pressureapplied to the control input of at least said relay valves bycontrolling said solenoid valves so as to adopt a second operatingcondition in which the first and second solenoid-operated switchingvalves are in their second and first conditions respectively, while thesolenoid-operated on/off valve associated with said at least one relayvalve is in said first condition.
 2. A system according to claim 1,further comprising pressure sensor means for supplying said electroniccontrol unit (ECU) with electrical signals indicating the value of thepressure at the control input, the supply inlet and the said first andsecond outputs of the system.
 3. A system according to claim 2, in whichadditional sensor means are connected to the electronic control unit(ECU) for supplying electrical signals indicating the load condition ofthe vehicle.